Grouting

ABSTRACT

A method of providing waterproof barriers in water bearing ground formations by means of grouting. Holes are drilled to outline the barrier and the formations between holes are presplit to provide artificial cracks or fissures. Subsequently grout is forced down the holes or other holes drilled in the same area so that the pre-split rock is impregnated with the grout.

Unite States Patent Muller 1541 GROUTING [72] Inventor: Donald Sinclair Muller, 2 Stirling Ave., Hurlingham, Johannesburg, Transvaal, South Africa 22 Filed: March 13,1970

21 Appl.No.: 19,302

[30] Foreign Application Priority Data March 13, 1969 Great Britain ..13,350/69 [52] US. Cl. ..61/36, 166/281, 166/286 [51] Int. Cl. ..E02d 3/12 [58] Field of Search ..61/35, 36, 53.64; 166/286,

[56] References Cited UNITED STATES PATENTS 1,009,159 11/1911 Lodwick ..61/36 R 1,449,236 3/1923 Malone ..61/53.54 2,313,109 3/1943 Wertz ..61/369 [451 Sept. 5, 1972 Primary Examiner-David J. Williamowsky Assistant Examiner-Philip C. Kannan Att0rney-Waters, Roditi, Schwartz & Nissen [5 7] ABSTRACT A method of providing waterproof barriers in water bearing ground formations by means of grouting. Holes are drilled to outline the barrier and the formations between holes are pre-split to provide artificial cracks or fissures. Subsequently grout is forced down the holes or other holes drilled in the same area so that the pre-split rock is impregnated with the grout.

10 Claims, 5 Drawing Figures man/M11 W PATENTEDSEP 5 I972 SHEET 1; OF 4 ll (I 1 31% iii ZiQqX EAA PKTENTEBSE 5 I SHEET 3 [1F 4 onotrrino This invention relates to grouting in water bearing ground formations to provide waterproof barriers such as are required, for example, for shaft linings or foun dations in construction work.

Grouting is a well-known technique. Boreholes are drilled in the zone in which the barrier is to be formed. A grouting composition which preferably is a cement grout but could be a chemical grout is injected into the boreholes in order to force the strata fluid out of the natural fissures and pores in the rock and to allow the grout to set and form a permanent seal.

Grouting techniques in their prior stage of development still offer serious operational disadvantages which derive from the inhomogeneity and discontinuity of natural rocks. Rocks of low permeability offer poor acceptance rates for injected material.

Various proposals have been made to overcome these disadvantages, but no single technique overcomes them all and not all of them in a satisfactory manner.

It is an object of the invention to make possible the provision of a waterproof barrier in geological formations with small pores and low permeability using any desired grout.

According to the invention a method of providing a water-proof barrier in rock strata in which holes are drilled in a zone in which the barrier is to be formed and grout is injected into the holes to form the barrier is characterized by the step of presplitting the stratum or strata in which the barrier is to be formed in the region which the barrier is to occupy.

By the term pre-splitting is meant the simultaneous application of fracturing pressures to adjacent holes of a series. in this way directionally controlled fractures are formed which extend between adjacent holes to provide a fracture plane or planes.

The grout may be a cement grout or it may be another grouting material. By forming artificial controlled cracks, the ground formation will then readily accept a grout such as a cement grout with relatively coarse particles.

The preferred method of pre-splitting the ground formation to form cracks is to drill holes in the ground, and then insert blasting charges in the holes to produce, on detonation, the required cracks. The holes can be drilled in a predetermined pattern with precision and the known pre-splitting blasting technique can be used to form a honeycomb of cracks in the desired position in the formation.

The pre-splitting blasting technique can be modified for particular purposes in the following way: Explosive charges which have the shape of a slim longitudinal column are formed with hollow grooves at the perimeter in longitudinal direction of the charge. Such explosive charges will detonate with the well-known hollowcharge effect, which focuses the explosives energy into and towards the hollow space during detonation. The longitudinal groove will create a longitudinal hollowcharge effect so that the transmission of the explosive energy is focused into pre-determined directions. The explosive charges have to be placed in the borehole in an oriented manner. This orientation can be achieved in various ways, eg by inserting a profiled recoverable plastic tube during the process of charging the boreholes. The application of a plastic tube can be combined with oriented cushioning of the explosive charge thus partially reducing the transmission of explosive energy towards undesirable directions. Such modifications increase the pre-splitting effect of of explosive charges in a borehole pattern.

Other methods of creating cracks are hydraulic fracturing using high pressure injections of fluids into the boreholes to cause the formation to crack under pressure; mechanical wedging or jacking; impulse fracturing (holes filled with fluid and a heavy instantaneous impulse applied at the top of the fluid to give a waterhammer" effect).

These alternative methods of pre-splitting can be used either on their own, or successively or in combination.

For example, the initial pre-split could be achieved by means of blasting, after which subsequent high pressure injection of fluids with suitable viscosity containing sized sand could jack-up and keep open the fractures. Thereafter, cement grouting would create bonding and sealing of the impermeable barrier zone.

The spacing of the holes and the method of fracturing depend upon the formation conditions encountered and the desired type of barrier to be formed.

A number of examples of this technique are illustrated diagrammatically in the accompanying drawings in which:

FlGS. l, 2 and 3 illustrate the formation of waterproof barriers in shaft sinking, eg for mines;

FIG. 4 illustrates the formation of waterproof barriers in tunnelling; and

FIG. 5 illustrates the formation of waterproof curtains.

FIG. 1 illustrates diagrammatically in section a typical ground formation in which a mine shaft, indicated by dashed lines 10, is to be sunk. Around the periphery of the mine shaft, holes ll are drilled, the holes being in two circles spaced apart and between which a waterproof barrier is formed. After these holes have been drilled, controlled pre-splitting using blasting as described above is employed to cause cracks throughout the region 12 where the barrier is required. Then cement grout is injected into this region via the boreholes.

It may be required to have a waterproof barrier across the bottom of the shaft, as shown in FIG. 2. In this case, further holes 14 are drilled to a depth below the required bottom level and the whole area 15 below the shaft bottom but within the region where the cylindrical barrier 12 is to be formed is also split by controlled blasting and injected with cement grout.

In both FIGS. 1 and 2, the holes 11 and 14 are fractured over their bottom length only to insure that the fracture zone occurs outside the perimeter of the proposed shaft. Each series of holes is arranged to overlap the previous series to insure that a continuous barrier is formed. The holes which have been used for the pre-splitting are also used for the cement grout injection to economize on drilling costs. However, separate holes may be drilled for grouting purposes if so desired.

Under normal circumstances conventional cement grout is used but if cement-aggressive waters exist in the formations special cements could be used to resist chemical attack. Chemical grout may be used alone or in combination with the cement grout if desired.

It may be desirable, as shown in FIGS. 1 and 2, to maintain a zone of unfractured rock between the zone of controlled fracture grouting and the area which is to be excavated, and to create a smooth surface of the excavation. This can be achieved by excavating the main shaft by means of drilling or cutting methods thus eliminating radial fracturing. If explosives have to be used for excavation, then methods of pre-splitting or smooth-blasting may be applied during the excavation process.

The zone of controlled fracture grouting however can form the immediate circumference of the area which is to be excavated. In such cases the techniques of improving the focusing of the pre-splitting energy into predetermined direction using explosives charges with hollow grooves in oriented arrangement thus creating a linear hollow charge effect could be used. Radial fracturing around the excavation area can in this way be reduced and smooth excavation surfaces can be created. In the same way radial fracturing around the pre-splitting zone can be reduced and a reasonably well controlled grout-treatment zone can be formed.

The method of controlled fracture grouting utilizing pre-splitting holes and injection holes can be applied for vertical, inclined or horizontal excavations with various linear wall shapes and inclinations. Controlled fracture grouting can have the form of circumferential wall treatment eg from the surface through the permeable water bearing strata zone in single stage or in staggered multiple stages finally linking up into impermeable strata; from impermeable strata in the same way through permeable water bearing strata finally. linking up into impermeable strata, and/or could have the form of plug-type treatment e. g. below the bottom of a shaft or for a mine shaft which is to be sunk through extensive permeable strata from circular sub-levels or ahead of the face of tunnels or inclines located in permeable water bearing strata.

FIG. 3 illustrates the formation, in multiple stages, of a waterproof barrier around a deep shaft. In this particular example, the uppermost layer of the ground strata is impermeable and the shaft is sunk to a level before starting drilling. Around the shaft, holes 21 are drilled in directions inclined to the vertical and close together to enable waterproof barriers 22 and 23 to be formed by controlled splitting and grouting. These barriers are of conical form lying outside the periphery of the required shaft. The shaft is then sunk within this barrier to a level indicated by the dashed line 2 3. Then further holes 25 can be drilled to form further barriers 26, 27. It will be noted that each successive barrier overlaps and is immediately adjacent the preceding barrier so that a continuous waterproof region is extended downwards into the ground. As shown in the drawing, the operation may be repeated until the required depth is reached.

In mine shaft constructions, the pre-splitting and injection holes can be drilled from sub-levels which are set out at a suitable radial distance around the shaft. Controlled fracture grouting and any subsequent grout ing operations which may be required to achieve complete sealing off in low permeable strata can, with this technique, be carried out simultaneously with shaft sinking. In the event of long term deterioration of the grout seals, such sub-levels will permit additional grouting without interference with shaft operation and shaft mainten n e.

FIG. 5 illustrates a similar technique applied to tunnelling. In this Figure, a tunnel 30 is being driven horizontally through the ground and it is required to form a waterproof barrier around the region where the tunnel is to pass through a permeable layer 31 of the strata. Before reaching this layer 31, from the tunnel, holes 32. are drilled, at angles off-set from the axis of the tunnel, to pass through this layer 31. The regions 33 between the holes are then pre-split to form cracks, as previously described, and grout is injected to form a continuous waterproof barrier around the required path of the tunnel through the permeable layer 31.

Controlled fracture grouting can be applied to form barriers in permeable waterbearing formations or strengthened zones of defined shape in less competent rocks, eg to create underground cut-off walls for dams or to create a foundation pattern in the ground prior to surface constructions. Such a construction is illustrated in FIG. 5 where, before building a darn 40, two cut-off curtains 41, 42 are formed by drilling holes 43, splitting the rock to produce cracks and then injecting grout as previously described.

I claim:

1. A method of providing a waterproof barrier in rock strata, said method comprising drilling holes in a zone in which the barrier is to be formed, simultaneously applying fracturing pressures to adjacent holes to produce directionally controlled fractures extending between adjacent holes in a region in which the barrier is to be formed, and injecting grout into the holes to form the barrier.

2. A method as claimed in claim l, in which fracturing pressures are achieved by mechanical jacking.

3. A method as claimed in claim 1, in which fracturing pressures are achieved by mechanical wedging.

4. A method as claimed in claim 1, in which fracturing pressures are achieved by impulse fracturing.

5. A method as claimed in claim 1, in which the grout is a cement grout.

6. A method as claimed in claim 1, in which the grout is a chemical grout.

'7. A method as claimed in claim 1 in which the fracturing pressures are obtained by inserting blasting charges into the holes and detonating the charges.

8. A method as claimed in claim 7, in which directional blasting is employed.

9. A method as claimed in claim 8, in which the hollow charge effect is used to obtain pre-splitting in desired directions.

10. A method as claimed in claim 1,. in which the fracturing pressures are achieved by causing hydraulic fracturing of the rock. 

1. A method of providing a waterproof barrier in rock strata, said method comprising drilling holes in a zone in which the barrier is to be formed, simultaneously applying fracturing pressures to adjacent holes to produce directionally controlled fractures extending between adjacent holes in a region in which the barrier is to be formed, and injecting grout into the holes to form the barrier.
 2. A method as claimed in claim 1, in which fracturing pressures are achieved by mechanical jacking.
 3. A method as claimed in claim 1, in which fracturing pressures are achieved by mechanical wedging.
 4. A method as claimed in claim 1, in which fracturing pressures are achieved by impulse fracturing.
 5. A method as claimed in claim 1, in which the grout is a cement grout.
 6. A method as claimed in claim 1, in which the grout is a chemical grout.
 7. A method as claimed in claim 1 in which the fracturing pressures are obtained by inserting blasting charges into the holes and detonating the charges.
 8. A method as claimed in claim 7, in which directional blasting is employed.
 9. A method as claimed in claim 8, in which the hollow charge effect is used to obtain pre-splitting in desired directions.
 10. A method as claimed in claim 1, in which the fracturing pressures are achieved by causing hydraulic fracturing of the rock. 